1. Field of the Invention
This invention relates to a new shock absorbing material and more particularly to a new shock absorber which may be used as an insole or as a midsole for an article of footwear.
The new shock absorber comprises a multi-cell membrane which may be used as an insole or a midsole or which may be embedded in a flexible envelope which is then used as a midsole or an insole.
2. Description of the Prior Art
For ease of reference, the following description of the prior art as well as the description of the preferred embodiment of the invention will be made with reference to a shoe, as a specific article of footwear. It is to be understood that the present invention is applicable to all forms of footwear, such as shoes, boots, skates and the like and is not restricted to any type of footwear.
In the past, various attempts have been made to design a shock absorbing structure for use in shoes which directly increases the comfort of the wearer and reduces damage to the foot during athletic exercises.
These devices tended to increase the shock absorbing and functional support characteristics of the shoe and included inserts, shock absorbing layers, gas-inflated midsoles and the like. These devices generally were attached to a shoe or inserted directly into the shoe.
Synthetic rubber and other elastomeric materials used as an integral part of a shock absorbing device are well known and in widespread use. For example, Dupont Company's Hytrel (trade mark) 4056 is widely used as a material from which cushion insoles are made. For example, the "Bostonian Golf Shoe" uses an insole of about 3/16" in thickness which has been molded into a block and cut to shape.
While such insoles have significantly helped to reduce stress and discomfort experienced during walking or running, they did not provide to any great degree, the required shock absorbing characteristics without increasing the inner sole thickness to an unacceptable amount.
Other ideas have been suggested which involve the manufacture of an insert for use as a part of a shoe or for use as an insole to be inserted into existing footwear. One such idea is disclosed in Canadian patent No. 1,099,506 issued on Apr. 4, 1981 to Rudy. This patent discloses the use of a membrane consisting of a plurality of interconnected, intercommunicable chambers which are inflated with a large molecule gas as an inflating medium to produce the desired cushioning effect While this invention provides shock absorbency, it has three serious drawbacks. First, as the inflation medium shifts between the chambers, the antero/posterior and mediolateral stability is compromised to the point of creating a severe wobbling effect which could lead to a serious injury. Secondly, in the case of a heavier person, the inflating medium (gas) will shift from the heel portion to the forward portion of the shoe during walking. This will result in a bottoming out phase which may be a direct cause of heel spurs, severe knee problems or other serious injury. The third drawback is obviously that any anomaly or leak in any one of the chambers leads directly to a failure of the entire system since the channels communicate with each other.
Another system based on different principles is shown in U.S. Pat. No. 4,535,553 granted to Nike, Inc. The invention disclosed in this patent shows a shock absorbing layer encased in an elastomeric foam. This sole layer insert comprises many transversely and longitudinally spaced projections which act as a shock absorber.
A further solution is that proposed in my Canadian patent No. 1,084,260 issued on Aug. 26, 1980. This patent discloses an improved shoe sole containing discrete air chambers which helped to overcome or reduce injuries suffered by athletes during the performance of athletic activities. My invention provided the required shock absorbency of an air cushion system, the stability of an independent air chamber shoe sole and resiliency to the shoe. The use of discrete air chambers disclosed in my prior patent is particularly useful as an integral part of a shoe such as a midsole, but it is not practical to use it as an accessory for existing footwear.